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Abstract:

A positive charging single-layer electrophotographic photoconductor
configured to serve as an image-bearing member for use in an
image-forming apparatus includes a photosensitive layer on a conductive
base, including a charge-generating material, a hole-transport material,
an electron-transport material, and a binder resin, in which the
photosensitive layer has a polysiloxane oil, with the amount of the
polysiloxane oil being in the range of about 0.005% by mass to about
0.021% by mass with respect to the total mass of materials.

Claims:

1. A positive charging single-layer electrophotographic photoconductor
configured to serve as an image-bearing member for use in an
image-forming apparatus, comprising: a photosensitive layer on a
conductive base, the photosensitive layer including a charge-generating
material, a hole-transport material, an electron-transport material, and
a binder resin, wherein the photosensitive layer includes a polysiloxane
oil in an amount at least about 0.005% by mass and not greater than about
0.021% by mass with respect to the total mass of materials.

2. The positive charging single-layer electrophotographic photoconductor
according to claim 1, wherein a surface of the photosensitive layer is
applied by a direct voltage with a contact charging method.

3. The positive charging single-layer electrophotographic photoconductor
according to claim 1, wherein the amount of polysiloxane oil is at least
about 0.005% by mass and not greater than about 0.016% by mass with
respect to the total mass of materials in the photosensitive layer.

4. The positive charging single-layer electrophotographic photoconductor
according to claim 1, wherein the polysiloxane oil is a
dimethylpolysiloxane oil.

5. The positive charging single-layer electrophotographic photoconductor
according to claim 1, wherein the polysiloxane oil has a
viscosity-average molecular weight of 1,000 to 10,000.

7. The positive charging single-layer electrophotographic photoconductor
according to claim 1, further comprising: an intermediate layer provided
between the conductive base and the photosensitive layer.

8. The positive charging single-layer electrophotographic photoconductor
according to claim 1, further comprising: a protective layer provided on
the photosensitive layer.

9. An image-forming apparatus comprising: an image-bearing member; a
charging portion configured to charge a surface of the image-bearing
member; an exposure portion configured to expose the charged
image-bearing member to form an electrostatic latent image on the surface
of the image-bearing member; a developing portion configured to develop
the electrostatic latent image to form a toner image; and a transfer
portion configured to transfer the toner image from the image-bearing
member to an object, wherein the image-bearing member comprises the
positive charging single-layer electrophotographic photoconductor
according to claim 1.

10. The image-forming apparatus according to claim 9, wherein the
charging portion is configured to apply a direct voltage by a contact
charging method.

11. The image-forming apparatus according to claim 9, wherein the
charging portion includes a charging roller configured to come into
contact with the surface of the positive charging single-layer
electrophotographic photoconductor to charge the photosensitive layer.

12. The image-forming apparatus according to claim 11, wherein a direct
voltage applied to the charging roller is in the range of 1000 V to 2000
V.

13. The image-forming apparatus according to claim 12, wherein the direct
voltage applied to the charging roller is in the range of 1200 V to 1800
V.

14. The image-forming apparatus according to claim 11, wherein the
charging roller includes a resin layer comprising a resin, wherein the
resin contains at least one of silicone resins, urethane resins, and
silicone-modified resins.

15. A method for forming an image, comprising: charging a surface of a
image-bearing member; exposing the charged image-bearing member to form
an electrostatic latent image on the surface of the image-bearing member;
developing the electrostatic latent image to form a toner image; and
transferring the toner image from the image-bearing member to an object,
wherein the image-bearing member comprises the positive charging
single-layer electrophotographic photoconductor according to claim 1.

16. A method for forming an image according to claim 15, wherein in the
charging of the surface of the image-bearing member, the surface of the
image-bearing member is applied by a direct voltage with a contact
charging method.

17. The method for forming an image according to claim 15, wherein in the
charging of the surface of the image-bearing member, a charging roller
charges the surface of the image-bearing member by a contact charging
method.

Description:

INCORPORATION BY REFERENCE

[0001] This application is based upon and claims the benefit of priority
from the corresponding Japanese Patent Application No. 2010-129454, filed
Jun. 4, 2010, the entire contents of which are incorporated herein by
reference.

FIELD

[0002] The present disclosure relates to a positive charging single-layer
electrophotographic photoconductor, an image-forming apparatus including
the positive charging single-layer electrophotographic photoconductor and
a method for forming an image.

BACKGROUND

[0003] Electrophotographic photoconductors for use in image-forming
apparatuses using electrophotographic methods include inorganic
photoconductors including photosensitive layers composed of inorganic
materials, such as selenium; and organic photoconductors including
photosensitive layers mainly composed of organic materials, such as
binder resins, charge-generating materials, and charge transport
materials. Among these photoconductors, organic photoconductors are
widely used because they are easily produced, materials for
photosensitive layers can be selected from a wide variety of materials,
and high design flexibility is provided, as compared with inorganic
photoconductors.

[0004] Examples of organic photoconductors include single-layer organic
photoconductors each provided with a photosensitive layer that contains a
charge-generating material and a charge transport material in the same
layer. It is known that single-layer organic photoconductors have simple
layer structures, are easily produced, and suppress the occurrence of
coating defects, as compared with multilayer organic photoconductors each
including a charge-generating layer containing a charge-generating
material and a charge transport layer containing a charge transport
material stacked on a conductive base. Because of these advantages,
single-layer organic photoconductors are increasingly being used.

[0005] Furthermore, it is known that the use of contact charging methods
in positive polarity serving as methods for charging electrophotographic
photoconductors of image-forming apparatuses significantly reduces the
amount of oxidizing gas generation, such as ozone, formed during
charging. So, a positive charging method in positive polarity is often
employed as a method for charging an electrophotographic photoconductor
of an image-forming apparatus in view of adverse effects on the lifetime
of photoconductors and office environments by the emission of the
oxidizing gas, such as ozone. Positive charging single-layer
electrophotographic photoconductors are increasingly being used from this
point of view.

[0006] However, photosensitive layers of organic photoconductors are
liable to wear because they are composed of soft organic materials. It is
known that, in particular, surface states are easily changed due to wear
during the initial use of organic photoconductors, thus causing a rapid
reduction in surface potential with wear, so that image defects are
liable to occur.

[0007] Additionally, in such contact charging methods, photosensitive
layers wear significantly, compared with non-contact charging methods. In
the case where positive charging single-layer electrophotographic
photoconductors are used in contact charging methods, surface potentials
are reduced during initial use, so that sufficient characteristics for
use in an image-forming apparatus are not obtained.

SUMMARY

[0008] According to an aspect of some embodiments of the present
disclosure, a positive charging single-layer electrophotographic
photoconductor configured to serve as an image-bearing member for use in
an image-forming apparatus includes a photosensitive layer on a
conductive base, including a charge-generating material, a hole-transport
material, an electron-transport material, and a binder resin, in which
the photosensitive layer comprises a polysiloxane oil, in an amount of at
least about 0.005% by mass and not greater than about 0.021% by mass with
respect to the total mass of materials. In various embodiments, the
image-forming apparatus may include a charging portion configured to
apply a direct voltage by a contact charging method to the image-bearing
member.

[0009] According to some aspects of the present disclosure, an
image-forming apparatus includes an image-bearing member, a charging
portion configured to charge a surface of the image-bearing member, an
exposure portion configured to expose the charged image-bearing member to
form an electrostatic latent image on the surface of the image-bearing
member, a developing portion configured to develop the electrostatic
latent image to form a toner image, and a transfer portion configured to
transfer the toner image from the image-bearing member to an object, in
which the image-bearing member is the positive charging single-layer
electrophotographic photoconductor described above.

[0010] According to some aspects of the present disclosure, a method for
forming an image includes charging a surface of the image-bearing member
by the contact charging method, exposing the charged image-bearing member
to form an electrostatic latent image on the surface of the image-bearing
member, developing the electrostatic latent image to form a toner image,
and transferring the toner image from the image-bearing member to an
object, in which the image-bearing member is the positive charging
single-layer electrophotographic photoconductor described above.

[0011] The above and other objects, features, and advantages of various
embodiments of the present disclosure will be more apparent from the
following detailed description of embodiments taken in conjunction with
the accompanying drawings.

[0012] In this text, the terms "comprising", "comprise", "comprises" and
other forms of "comprise" can have the meaning ascribed to these terms in
U.S. Patent Law and can mean "including", "include", "includes" and other
forms of "include". The phrase "an embodiment" as used herein does not
necessarily refer to the same embodiment, though it may. In addition, the
meaning of "a," "an," and "the" include plural references; thus, for
example, "an embodiment" is not limited to a single embodiment but refers
to one or more embodiments. As used herein, the term "or" is an inclusive
"or" operator, and is equivalent to the term "and/or," unless the context
clearly dictates otherwise. The term "based on" is not exclusive and
allows for being based on additional factors not described, unless the
context clearly dictates otherwise.

[0013] Various features of novelty which characterize various aspects of
the disclosure are pointed out in particularity in the claims annexed to
and forming a part of this disclosure. For a better understanding of the
disclosure, operating advantages and specific objects that may be
attained by some of its uses, reference is made to the accompanying
descriptive matter in which exemplary embodiments of the disclosure are
illustrated in the accompanying drawings in which corresponding
components are identified by the same reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following detailed description, given by way of example, but
not intended to limit the disclosure solely to the specific embodiments
described, may best be understood in conjunction with the accompanying
drawings, in which:

[0015] FIGS. 1A to 1C are schematic diagrams each illustrating the
structure of a positive charging single-layer electrophotographic
photoconductor according to an embodiment of the present disclosure;

[0016] FIG. 2 is a schematic diagram illustrating the structure of an
image-forming apparatus including a positive charging single-layer
electrophotographic photoconductor according to an embodiment of the
present disclosure; and

[0017] FIG. 3 is a graph illustrating the relationship between the
polysiloxane oil amount of a photosensitive layer and the amount of
reduction in surface potential in an experimental example according to
some embodiments of the present disclosure.

DETAILED-DESCRIPTION

[0018] Reference will now be made in detail to various embodiments of the
disclosure, one or more examples of which are illustrated in the
accompanying drawings. Each example is provided by way of explanation of
the disclosure, and by no way limiting the present disclosure. In fact,
it will be apparent to those skilled in the art that various
modifications, combinations, additions, deletions and variations can be
made in the various embodiments of the disclosure without departing from
the scope or spirit of the present disclosure. For instance, features
illustrated or described as part of one embodiment can be used in another
embodiment to yield a still further embodiment. It is intended that the
present disclosure covers such modifications, combinations, additions,
deletions, applications and variations that come within the scope of the
appended claims and their equivalents.

[0019] Some embodiments relate to a positive charging single-layer
electrophotographic photoconductor configured to serve as an
image-bearing member for use in an image-forming apparatus that includes
a charging portion configured to apply a direct voltage by a contact
charging method, the positive charging single-layer electrophotographic
photoconductor including a photosensitive layer on a conductive base,
with the photosensitive layer including a charge-generating material, a
hole-transport material, an electron-transport material, and a binder
resin, in which the photosensitive layer has a polysiloxane oil, amount
of polysiloxane oil ranging about 0.005% by mass to about 0.021% by mass
with respect to the total mass of materials of the photosensitive layer.
As indicated in the background section, and as understood by those
skilled in the art, a single-layer electrophotographic photoconductor as
used herein refers to an electrophotographic photoconductor in which the
charge-generating and charge-transport functions are provided in the same
layer, although the single-layer electrophotographic photoconductor may
comprise two or more layers.

[0020] Referring to FIGS. 1A to 1C, a positive charging single-layer
electrophotographic photoconductor 10 according to an embodiment of the
present disclosure includes a conductive base 12 and a photosensitive
layer 14 arranged on the conductive base 12, the photosensitive layer 14
having a single-layer structure and comprising a charge-generating
material, a hole-transport material and an electron-transport material as
a charge transport material, and a binder resin. The positive charging
single-layer electrophotographic photoconductor 10 comprising the
conductive base 12 and the photosensitive layer 14 is not particularly
limited, and may comprise one or more additional layers.

[0021] Specifically, for example, as illustrated in FIG. 1A, in some
embodiments the photosensitive layer 14 may be arranged directly on the
conductive base 12. As illustrated in FIG. 1B, some embodiments may
include an intermediate layer 16 arranged between the conductive base 12
and the photosensitive layer 14. As illustrated in FIGS. 1A and 1B, the
photosensitive layer 14 may serve as an outermost layer. As illustrated
in FIG. 1C, in some embodiments a protective layer 18 may be arranged on
the photosensitive layer 14. These illustrative embodiments are not
exclusive; for example, embodiments may comprise one or more layers
disposed between photosensitive layer 14 and conductive base 12 and may
alternatively or additionally comprise one or more layers disposed on or
above the upper surface of photosensitive layer 14 (i.e., this "upper
surface," with reference to the views in FIGS. 1A-1C; being the surface
of photosensitive layer 14 that is farthest from conductive base 12).

[0022] Illustrative embodiments of the conductive base and the
photosensitive layer are described below.

[0023] The conductive base according to an embodiment of the present
disclosure is not particularly limited as long as it can be used as a
conductive base of the positive charging single-layer electrophotographic
photoconductor.

[0024] A conductive base is a component having at least a surface
comprising an electrically conductive material. For example, a component
comprising essentially entirely of an electrically conductive material
may be used as the conductive base. Alternatively, a component
comprising, for example, a plastic or other insulating or dielectric
material, and having a surface covered with an electrically conductive
material may be used as the conductive base.

[0026] These, and other, conductive materials may be used separately or in
combination as, for example, an alloy of two or more.

[0027] Among these materials, aluminum or an aluminum alloy may be
preferable or particularly well-suited for implementing some embodiments
of the conductive base. Such embodiments may provide a positive charging
single-layer electrophotographic photoconductor that may be capable of
forming a more preferred image in some implementations.

[0028] A possible reason for preferred images possibly being provided by
some implementations of a positive charging single-layer
electrophotographic photoconductor employing an aluminum or aluminum
alloy conductive base is that, in some implementations, using such a
conductive base provides for charges being satisfactorily transferred
from the photosensitive layer to the conductive base.

[0029] The shape of the conductive base may be appropriately selected,
depending on the structure of an image-forming apparatus used. Examples
of the shape of the base that can be used include sheets and drums.

[0030] In accordance with some embodiments, the photosensitive layer
included in the positive charging single-layer electrophotographic
photoconductor is not particularly limited as long as the photosensitive
layer has a single-layer structure, contains a charge-generating
material, a hole-transport material, an electron-transport material, and
a binder resin, and has a polysiloxane oil in an amount ranging from
about 0.005% by mass to about 0.021% by mass with respect to the total
mass of the materials.

[0031] In some embodiments, in the case of an image-forming apparatus
including a charging portion configured to apply a direct voltage by a
contact charging method, the presence of the polysiloxane oil in the
photosensitive layer in an amount within the range described above
suppresses a reduction in surface potential during initial use when the
positive charging single-layer electrophotographic photoconductor is
used. In this respect, it is understood that the above specified
approximate limits for the range of polysiloxane oil reflect, for
example, not only measurement error and/or nominal variations, but also
deviations from the specified values that do not result in a
substantially degraded characteristic with respect to suppressing surface
potential reduction. In various embodiments, however, such
surface-potential-reduction suppression characteristics are associated
with having polysiloxane oil in an amount ranging from about 0.005% by
mass to about 0.021% by mass with respect to the total mass of the
materials in the photosensitive layer, these values nonetheless
reflecting measurement error and/or nominal variations.

[0032] So, the selection of the materials for the photosensitive layer in
the positive charging single-layer electrophotographic photoconductor is
not significantly limited. Furthermore, when the polysiloxane amount of
the photosensitive layer falls within the above range, a defect in the
photosensitive layer is less likely to occur.

[0033] The polysiloxane oil, the charge-generating material, the
hole-transport material, the electron-transport material, the binder
resin, and additives, which are components included in the photosensitive
layer, will be described below with respect to various illustrative
embodiments. Furthermore, a method for producing a positive charging
single-layer electrophotographic photoconductor will be described below
in accordance with some embodiments.

[0034] In view of the present disclosure, it will be understood that
various polysiloxane oils may be used, without limitation, in the
positive charging single-layer electrophotographic photoconductor to
provide the desired characteristics. Some examples of the polysiloxane
oil include organopolysiloxane represented by general formula (1):

##STR00001##

(wherein R's may be the same or different, and each represent an alkyl
group having 1 to 6 carbon atoms or a phenyl group; X's may be the same
or different, and each represent a group selected from the group
consisting of alkyl groups each having 1 to 6 carbon atoms, a phenyl
group, modified reactive groups, and modified nonreactive groups; Y
represents a modified reactive group or a modified nonreactive group, and
when a plurality of Y's are present, Y's may be the same or different; m
represents an integer of 1 or more; and n represents an integer of 0 or
more).

[0035] When each X or Y represents a modified reactive group or a modified
nonreactive group contained in the polysiloxane oil represented by
general formula (1), specific illustrative examples thereof include those
described below.

[0036] Examples of the modified reactive group include:

##STR00002##

(wherein R1 to R8 each represent a single bond or an alkylene
group having 1 to 6 carbon atoms).

[0037] Examples of the modified nonreactive group include:

##STR00003##

(wherein R9 and R14 each represent a single bond or an alkylene
group having 1 to 6 carbon atoms; R10 represents an alkyl group
having 1 to 6 carbon atoms; R11 represents an alkylene group having
1 to 6 carbon atoms; R12, R13, and R15 each represent an
alkyl group having 7 to 20 carbon atoms; a and b each represent an
integer of 0 or more, and the sum of a and b is 1 or more; c represents
an integer of 1 to 6, d represents an integer of 0 or more, e represents
an integer of 1 or more, and the relationship d+e=2c+1 is satisfied).

[0038] The polysiloxane oil used in an embodiment of the present
disclosure may contain the following branch chain in a molecular chain:

##STR00004##

[0039] The viscosity-average molecular weight of the polysiloxane oil used
in an embodiment of the present disclosure is not particularly limited
provided the desired characteristics of the single-layer
electrophotographic photoconductor are achieved. In some embodiments, the
polysiloxane oil has a viscosity-average molecular weight of 1,000 to
10,000. The viscosity-average molecular weight (M) can be calculated
from, for example, the A. J. Barry formula
(log(η)=1.00+0.0123M0.5) described in J. Appl. Phys. 17, 1020
(1946) using the viscosity of the polysiloxane oil.

[0040] In some embodiments, dimethylpolysiloxane oil is particularly
well-suited as the polysiloxane oil.

[0042] These charge-generating materials may be used separately or in
combination of two or more so as to have an absorption wavelength in a
desired region. Among these charge-generating materials, in particular,
for digital optical image-forming apparatuses, such as laser beam
printers and facsimiles, provided with light sources, such as
semiconductor lasers, photoconductors sensitive in the wavelength range
of 700 nm or more are required. So, for example, phthalocyanine pigments,
such as metal-free phthalocyanine and oxotitanylphthalocyanine, are
preferably used in some embodiments.

[0043] Note that various crystal forms of the phthalocyanine pigments may
be used without limitation. Furthermore, for analog optical image-forming
apparatuses, such as electrostatic copiers, provided with white light
sources, such as halogen lamps, photoconductors sensitive in the visible
range are required. So, for example, perylene pigments and bisazo
pigments are preferably used in some such implementations.

[0044] The hole-transport material is not particularly limited as long as
it can be used as a hole-transport material contained in the
photosensitive layer of the positive charging single-layer
electrophotographic photoconductor.

[0045] Specific examples of the hole-transport material that may be used
in some embodiments include benzidine derivatives; oxadiazole compounds,
such as 2,5-di-(4-methylaminophenyl)-1,3,4-oxadiazole; styryl compounds,
such as 9-(4-diethylaminostyryl)anthracene; carbazole compounds, such as
polyvinylcarbazole; organic polysilane compounds; pyrazoline compounds,
such as 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline; hydrazone
compounds; triphenylamine compounds; nitrogen-containing cyclic
compounds, such as indole compounds, oxazole compounds, isoxazole
compounds, thiazole compounds, and triazole compounds; and fused
polycyclic compounds. Among these hole-transport materials,
triphenylamine compounds, each having one or more triphenylamine
skeletons in a molecule, may be preferred for some embodiments.

[0046] These hole-transport materials may be used separately or in
combination of two or more.

[0047] The electron-transport material is not particularly limited as long
as it can be used as an electron-transport material contained in the
photosensitive layer of the positive charging single-layer
electrophotographic photoconductor.

[0049] The electron-transport materials may be used separately or in
combination of two or more.

[0050] The binder resin is not particularly limited as long as it can be
used as a binder resin contained in the photosensitive layer of the
positive charging single-layer electrophotographic photoconductor.

[0053] The photosensitive layer of the positive charging single-layer
electrophotographic photoconductor may contain various additives to the
extent that electrophotographic characteristics are not adversely
affected, in addition to the polysiloxane oil, the charge-generating
material, the hole-transport material, the electron-transport material,
and the binder resin. Examples of additives that can be added to the
photosensitive layer according to some embodiments include
antidegradants, such as antioxidants, radical scavengers, singlet
quenchers and ultraviolet absorber, softeners, plasticizers, surface
modifiers, extenders, thickeners, dispersion stabilizers, wax, acceptors,
donors, surfactants, and leveling agents.

[0054] In accordance with some embodiments, a method for producing the
positive charging single-layer electrophotographic photoconductor is not
particularly limited as long as the desired characteristics of the
single-layer electrophotographic photoconductor are achieved. An
illustrative method, which in some cases may be preferred, for producing
the positive charging single-layer electrophotographic photoconductor is
a method including applying a coating liquid for the photosensitive layer
onto the conductive base to form the photosensitive layer. Specifically,
in some embodiments, a coating liquid in which the polysiloxane oil, the
charge-generating material, the hole-transport material, the
electron-transport material, the binder resin, and, optionally, various
additives are dissolved or dispersed in a solvent, is applied onto the
conductive base and dried to produce the photoconductor.

[0055] An application method is not particularly limited. Examples thereof
include methods using spin coaters, applicators, spray coaters, bar
coaters, dip coaters, and doctor blades. An example of a method for
drying the coating film formed on the conductive base is a method in
which hot-air drying is performed at 80° C. to 150° C. for
15 minutes to 120 minutes.

[0056] In the positive charging single-layer electrophotographic
photoconductor according to some embodiments, the photosensitive layer
has a polysiloxane oil, amount of polysiloxane oil ranging from about
0.005% by mass to about 0.021% by mass and preferably from 0.005% by mass
to 0.016% by mass with respect to the total mass of the materials. In
some embodiments, in the case where a direct voltage is applied by a
contact charging method, the presence of the polysiloxane oil in the
photosensitive layer in an amount within the range described above
stabilizes the amount of the charge of the positive charging single-layer
electrophotographic photoconductor during initial use without causing a
defect on a surface of the positive charging single-layer
electrophotographic photoconductor.

[0057] In the positive charging single-layer electrophotographic
photoconductor, proportions of the charge-generating material, the
hole-transport material, the electron-transport material, and the binder
resin are appropriately determined and are not particularly limited.
While these proportions are not particularly limited, the following
nevertheless provides illustrative ranges that may be implemented in some
embodiments.

[0058] Specifically, for example, in some embodiments, the proportion of
the charge-generating material is preferably in the range of 0.1 parts by
mass to 50 parts by mass and more preferably 0.5 parts by mass to 30
parts by mass with respect to 100 parts by mass of the binder resin.

[0059] Additionally, in some embodiments the proportion of the
electron-transport material is preferably in the range of 5 parts by mass
to 100 parts by mass and more preferably 10 parts by mass to 80 parts by
mass with respect to 100 parts by mass of the binder resin.

[0060] Further, in various embodiments the proportion of the
hole-transport material is preferably in the range of 5 parts by mass to
500 parts by mass and more preferably 25 parts by mass to 200 parts by
mass with respect to 100 parts by mass of the binder resin.

[0061] In some embodiments, the total amount of the hole-transport
material and the electron-transport material, i.e., the amount of the
charge transport material, is preferably in the range of 20 parts by mass
to 500 parts by mass and more preferably 30 parts by mass to 200 parts by
mass with respect to 100 parts by mass of the binder resin.

[0062] The thickness of the photosensitive layer of the positive charging
single-layer electrophotographic photoconductor is not particularly
limited as long as the photosensitive layer functions sufficiently as a
photosensitive layer.

[0063] Specifically, by way of example, in some embodiments the
photosensitive layer preferably may have a thickness of 5 μm to 100
μm and more preferably 10 μm to 50 μm.

[0064] The solvent contained in the coating liquid for the photosensitive
layer is not particularly limited as long as the materials constituting
the photosensitive layer can be dissolved or dispersed therein. Specific
examples thereof that may be used in some embodiments include alcohols,
such as methanol, ethanol, isopropanol, and butanol; aliphatic
hydrocarbons, such as n-hexane, octane, and cyclohexane; aromatic
hydrocarbons, such as benzene, toluene, and xylene; halogenated
hydrocarbons, such as dichloromethane, dichloroethane, carbon
tetrachloride, and chlorobenzene; ethers, such as dimethyl ether, diethyl
ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene
glycol dimethyl ether; ketones, such as acetone, methyl ethyl ketone,
methyl isobutyl ketone, and cyclohexanone; esters, such as ethyl acetate
and methyl acetate; and aprotic polar organic solvents, such as
dimethylformaldehyde, dimethylformamide, and dimethyl sulfoxide. These
solvents may be used separately or in combination of two or more.

[0065] The positive charging single-layer electrophotographic
photoconductor may be used as an image-bearing member for use in an
image-forming apparatus that includes a charging portion configured, in
some embodiments, to apply a direct voltage by a contact charging method
as described below (though it may be used in an image forming apparatus
that employs non-contact charging). In such implementations, the positive
charging single-layer electrophotographic photoconductor according to
some embodiments results in the stabilization of the surface potential of
the positive charging single-layer electrophotographic photoconductor
during initial use even under conditions in which the charging portion
configured to apply a direct voltage by the contact charging method is
used, i.e., the surface potential is less likely to be stabilized.
Thereby, it is possible to provide the image-forming apparatus that
suppresses the occurrence of image defects.

[0066] Some embodiments of the present disclosure also relate to an
image-forming apparatus that includes an image-bearing member, a charging
portion configured to apply a direct voltage by a contact charging method
to charge a surface of the image-bearing member, an exposure portion
configured to expose the charged image-bearing member to form an
electrostatic latent image on the surface of the image-bearing member, a
developing portion configured to develop the electrostatic latent image
to form a toner image, and a transfer portion configured to transfer the
toner image from the image-bearing member to an object, such as a paper,
in which a positive charging single-layer electrophotographic
photoconductor according to the foregoing discussed embodiments is used
as the image-bearing member.

[0067] The image-forming apparatus according to such embodiments of the
present disclosure can be used for any of monochrome-image-forming
apparatuses and color-image-forming apparatuses. Here, by way of example,
an embodiment of a tandem-type color image-forming apparatus using a
plurality of color toners will be described.

[0068] The image-forming apparatus including the positive charging
single-layer electrophotographic photoconductor according to this
embodiment includes a plurality of image-bearing members which are
juxtaposed to each other in a predetermined direction and which are
configured to form toner images using toners of different colors; and a
plurality of developing portions including developing rollers which face
the respective image-bearing members and which are configured to transfer
the toners attached on surfaces thereof and feed the toners onto surfaces
of the respective image-bearing members, in which a positive charging
single-layer electrophotographic photoconductor according to the
foregoing discussed embodiments is used as each of the image-bearing
members.

[0069] FIG. 2 is a schematic diagram illustrating an embodiment of a
tandem-type image-forming apparatus including a positive charging
single-layer electrophotographic photoconductor according to the
foregoing discussed embodiments of the present disclosure.

[0070] Here, an image-forming apparatus will be described by taking a
color printer 1 as an example.

[0071] As illustrated in FIG. 2, the color printer 1 includes a box-shaped
main body 1a. The box-shaped main body 1a is provided with a paper feed
portion 2 configured to feed paper P, an image-forming portion 3
configured to transfer a toner image on the paper P on the basis of, for
example, image data while the paper P fed from the paper feed portion 2
is being transferred, and a fusing portion 4 configured to perform fusing
treatment in which the unfused toner image transferred on the paper P in
the image-forming portion 3 is fused on the paper P. Furthermore, a
paper-ejecting portion 5 to which the paper P subjected to the fusing
treatment in the fusing portion 4 is ejected is arranged on the upper
surface of the main body 1a.

[0073] The paper feed cassette 121 configured to store different sized
sheets of paper P is detachably arranged in the main body 1a. The pickup
roller 122 is arranged at the upper left of the paper feed cassette 121
as illustrated in FIG. 2 and picks up the paper P, sheet by sheet, stored
in the paper feed cassette 121.

[0074] The paper feed rollers 123, 124, and 125 feed the paper P picked up
by the pickup roller 122 to a paper conveying path. The registration
roller 126 temporarily holds the paper P fed by the paper feed rollers
123, 124, and 125 to the paper conveying path, and then feeds the paper P
to the image-forming portion 3 at a predetermined time.

[0075] The paper feed portion 2 further includes a manual feed tray (not
shown) attached to the left side of the main body 1a illustrated in FIG.
2; and a pickup roller 127. The pickup roller 127 picks up the paper P
placed in the manual feed tray.

[0076] The paper P picked up by the pickup roller 127 is fed by the paper
feed rollers 123 and 125 to the paper conveying path and then fed by the
registration roller 126 to the image-forming portion 3 at a predetermined
time.

[0077] The image-forming portion 3 includes an image-forming unit 7, an
intermediate transfer belt 31 in which a toner image formed on the basis
of image data transmitted from, for example, a computer is primarily
transferred by the image-forming unit 7 onto a surface (contact surface),
and a secondary transfer roller 32 configured to secondarily transfer the
toner image formed on the intermediate transfer belt 31 onto the paper P
fed from the paper feed cassette 121.

[0078] The image-forming unit 7 includes a unit 7K for black toner
development, a unit 7Y for yellow toner development, a unit 7C for cyan
toner development, and a unit 7M for magenta toner development
sequentially arranged from the upstream side (right side in FIG. 2) to
the downstream side.

[0079] A positive charging single-layer electrophotographic photoconductor
37 (hereinafter, referred to as a "photoconductor 37") configured to
serve as an image-bearing member is arranged at the center of each of the
units 7K, 7Y, 7C, and 7M so as to be rotated in the direction indicated
by an arrow (in a clockwise direction).

[0080] A charging portion 39, an exposure portion 38, a developing portion
71, a cleaning portion (not shown), a charge eliminator (not shown) as a
charge eliminating portion, and so forth are arranged around each of the
photoconductors 37 from the upstream side along the rotational direction.
As the photoconductor 37, a positive charging single-layer
electrophotographic photoconductor according to the hereinabove described
embodiments is used.

[0081] The charging portion 39 uniformly charges the circumferential face
of the photoconductor 37 that rotates in the direction indicated by the
arrow. A specific example of the charging portion 39 is a portion in
which a charging roller charges the circumferential face (surface) of the
photoconductor 37 while the portion is in contact with the photoconductor
37. The charging portion 39 including the charging roller is preferably
used in various embodiments.

[0082] An example of the charging roller is a roller that rotates in
response to the rotation of the photoconductor 37 while the roller is in
contact with the photoconductor 37. A roller having at least a surface
portion composed of a resin is exemplified.

[0083] More specifically, a roller is exemplified which includes a mandrel
rotatably supported, a resin layer arranged on the mandrel, and a
voltage-applying portion configured to apply a voltage to the mandrel.
The charging portion including the charging roller charges the surface of
the photoconductor 37 in contact with the resin layer by the application
of a voltage to the mandrel using the voltage-applying portion.

[0084] In various embodiments such as that presently described, a voltage
applied by the voltage-applying portion to the charging roller is only a
direct voltage. As described above, in the case where only a direct
voltage is applied to the charging roller, the wear amount of the
photosensitive layer tends to be small, compared with the case where an
alternating voltage or a superimposed voltage in which an alternating
voltage is superimposed on a direct voltage.

[0085] So, in accordance with various embodiments, the positive charging
single-layer electrophotographic photoconductor provides for the
suppression of the change of the surface state of the photosensitive
layer of the positive charging single-layer electrophotographic
photoconductor due to wear during initial use, and thus results in the
stabilization of the surface potential of the photoconductor 37. In
various implementations, the direct voltage applied to the positive
charging single-layer electrophotographic photoconductor may preferably
be in the range of 1000 V to 2000 V, more preferably 1200 V to 1800 V,
and particularly preferably 1400 V to 1600 V.

[0086] In the case where an image-forming apparatus includes a charging
portion provided with a charging roller configured to apply a direct
voltage, and a positive charging single-layer electrophotographic
photoconductor configured to serve as an image-bearing member, the
surface potential of the positive charging single-layer
electrophotographic photoconductor 37 during initial use is less likely
to be stable because the charging efficiency of the contact charging
method is lower than that of a non-contact charging method. However, the
use of the positive charging single-layer electrophotographic
photoconductor according to the herein described embodiments as an
image-bearing member results in the stabilization of the surface
potential of the photoconductor 37, thereby suppressing the occurrence of
image defects.

[0087] A resin used for the resin layer of the charging roller is not
particularly limited as long as it can satisfactorily charge the
circumferential face of the photoconductor 37. Specific examples of the
resin used for the resin layer according to some embodiments include
silicone resins, urethane resins, and silicone-modified resins. The resin
layer may contain an inorganic filler.

[0088] The exposure portion 38 is what is called a laser scanning unit
configured to irradiate the circumferential face of the photoconductor 37
uniformly charged by the charging portion 39 with laser light on the
basis of image data input from a personal computer (PC) to form an
electrostatic latent image on the photoconductor 37.

[0089] The developing portion 71 feeds a toner onto the circumferential
face of the photoconductor 37 on which the electrostatic latent image has
been formed, thereby forming a toner image on the basis of the image
data. The resulting toner image is primarily transferred to the
intermediate transfer belt 31.

[0090] The cleaning portion removes the remaining toner on the
circumferential face of the photoconductor 37 after the primary transfer
of the toner image to the intermediate transfer belt 31.

[0091] The charge eliminator eliminates the charge on the circumferential
face of the photoconductor 37 after the completion of the primary
transfer. The circumferential face of the photoconductor 37 that has been
subjected to cleaning by the cleaning portion and neutralizing by the
charge eliminator rotates to the charging portion for next charging
treatment and is then subjected to another charging treatment in the
charging portion.

[0092] The intermediate transfer belt 31 is an endless belt that is
stretched over plural rollers, such as a driving roller 33, a driven
roller 34, a backup roller 35, and primary transfer rollers 36, in such a
manner that a surface (contact surface) of the intermediate transfer belt
31 is in contact with the circumferential face of each of the
photoconductors 37.

[0093] The intermediate transfer belt 31 is configured to run endlessly
over the plural rollers while the intermediate transfer belt 31 is
pressed against the photoconductor 37 by the primary transfer rollers 36
that face the respective photoconductors 37.

[0094] The driving roller 33 is rotationally powered by a driving source,
such as a stepping motor, and provides a driving force to cause the
intermediate transfer belt 31 to run endlessly. The driven roller 34, the
backup roller 35, and the primary transfer rollers 36 are rotatably
arranged and are rotationally driven by the driving roller 33 via the
endless run of the intermediate transfer belt 31. These rollers 34, 35,
and 36 are rotationally driven by the rotation of the driving roller 33
via the intermediate transfer belt 31 and support the intermediate
transfer belt 31.

[0095] The primary transfer rollers 36 apply a primary transfer bias (a
polarity opposite to a charge polarity of toners) to the intermediate
transfer belt 31. The toner images formed on the photoconductors 37 are
sequentially transferred (primarily transferred) to the intermediate
transfer belt 31 in a superposition manner at positions between the
photoconductors 37 and the respective primary transfer rollers 36, the
intermediate transfer belt 31 running in the direction indicated by the
arrow (counterclockwise) by the driving of the driving roller 33.

[0096] The secondary transfer roller 32 applies a secondary transfer bias,
which has a polarity opposite to that of the toner image, to the sheet P.
The toner image primarily transferred to the intermediate transfer belt
31 is transferred to the sheet P at a position between the secondary
transfer roller 32 and the backup roller 35, thereby transferring a color
transfer image (unfused toner image) on the paper P.

[0097] The fusing portion 4 is configured for subjecting the transfer
image transferred to the paper P in the image-forming portion 3 to fusing
treatment. The fusing portion 4 includes a heating roller 41 heated by an
electric heating member and a pressing roller 42 which faces the heating
roller 41 and which has a circumferential face that is pressed against
the circumferential face of the heating roller 41. The transfer image
transferred to the paper P by the secondary transfer roller 32 in the
image-forming portion 3 is subjected to fusing treatment by heating when
the paper P is passed between the heating roller 41 and the pressing
roller 42, thereby fusing the image on the paper P.

[0098] The fused paper P is ejected to the paper ejecting portion 5.

[0099] In the color printer 1 according to this illustrative embodiment,
conveying rollers 6 are appropriately arranged between the fusing portion
4 and the paper ejecting portion 5.

[0100] The paper ejecting portion 5 is a recessed portion located on the
top of the main body 1a of the color printer 1. A paper output tray 51
configured to receive the ejected paper P is arranged on the bottom of
the recessed portion.

[0101] The color printer 1 forms an image on the paper P by the foregoing
image-forming operations. Such a tandem-type image-forming apparatus
described above includes the positive charging single-layer
electrophotographic photoconductor according to the hereinabove
embodiments as an image-bearing member. Accordingly, in some embodiments,
the image-foaming apparatus is configured to suppress a rapid reduction
in the surface potential of the positive charging single-layer
electrophotographic photoconductor during initial use and forms a
suitable image even under conditions in which a direct voltage is applied
by the contact charging method, which charging method generally does not
always provide satisfactory charging efficiency, i.e., the surface
potential of the photoconductor is less likely to be stabilized (e.g.,
compared to non-contact charging).

EXAMPLES

[0102] While the present disclosure will be described in further detail
below by examples, the present disclosure and the claimed subject matter
are not limited to or by the examples.

Example 1

[0103] Metal-free phthalocyanine (5 parts by mass), a hole-transport
material (HTM-1) of the following formula (50 parts by mass), an
electron-transport material (ETM-1) of the following formula (35 parts by
mass), dimethylpolysiloxane oil (trade name: KF-96-50cs,
viscosity-average molecular weight: 3200, manufactured by Shin-Etsu
Chemical Co., Ltd.) (0.01 parts by mass), a bisphenol Z-type
polycarbonate resin with a viscosity-average molecular weight of 50,000
(100 parts by mass), and tetrahydrofuran (800 parts by mass) were charged
into a ball mill. The mixture was subjected to dispersion treatment for
50 hours to prepare a coating liquid for a photosensitive layer. The
resulting coating liquid was applied by dip coating onto a conductive
base, which was a cylindrical aluminum tube having a diameter of 30 mm,
and dried at 100° C. for 40 minutes to remove tetrahydrofuran from
the coating film, thereby forming a positive charging single-layer
electrophotographic photoconductor including a photosensitive layer that
had a thickness of 30 μm:

##STR00006##

Examples 2 to 4 and Comparative Examples 1 to 4

[0104] Positive charging single-layer electrophotographic photoconductors
were produced as in Example 1, except that the amounts of the
dimethylpolysiloxane oil shown in Table 1 were used. Note that the
amounts shown in Table 1 indicate percent by mass of the
dimethylpolysiloxane oil contained in the photosensitive layer with
respect to the total mass of the photosensitive layer.

[0105] Each of the positive charging single-layer electrophotographic
photoconductors produced in these Examples and Comparative Examples was
attached to a printer (Model: FS-05300DN, manufactured by KYOCERA MITA
Corporation) including a charging roller that applied a direct voltage to
a charging portion. The amount of a reduction in surface potential, which
indicates the potential stability, and images were evaluated according to
methods described below. Table 1 shows the evaluation results.

[0106] The difference in surface potential between the positive charging
single-layer electrophotographic photoconductor at the start of endurance
printing and the positive charging single-layer electrophotographic
photoconductor after performing the endurance printing for 1 hour was
measured to evaluate the reduction in the surface potential of the
photosensitive layer with time during initial use.

[0107] After performing endurance printing for 1 hour, images formed by
printing were observed to evaluate the presence or absence of the
occurrence of an image defect. Evaluation criteria are described below.

[0108] Pass: No image defect was observed.

[0109] Failure: An image defect was observed.

[0110] Surfaces of the photosensitive layers of the positive charging
single-layer electrophotographic photoconductors produced in the Examples
and Comparative Examples were visually observed to evaluate the leveling
property. Evaluation criteria are described below.

[0111] Pass: A crater was not formed on the surface of the photosensitive
layer.

[0112] Failure: A crater was formed on the surface of the photosensitive
layer.

[0113] FIG. 3 illustrates the relationship between the amount of
polysiloxane oil in the photosensitive layer and the amount of the
reduction in the surface potential of the positive charging single-layer
electrophotographic photoconductor after performing the endurance
printing for 1 hour from the results of the Examples and Comparative
Examples.

[0114] FIG. 3 demonstrates that a polysiloxane oil amount of the
photosensitive layer of 0.021% by mass or less results in the suppression
of the reduction in the surface potential of the positive charging
single-layer electrophotographic photoconductor after performing the
endurance printing for 1 hour.

[0115] The results demonstrate that a polysiloxane oil amount of the
photosensitive layer of 0.016% by mass or less results in further
suppression of the reduction in the surface potential of the positive
charging single-layer electrophotographic photoconductor after performing
the endurance printing for 1 hour.

[0116] In the positive charging single-layer electrophotographic
photoconductor produced in each of Examples 1 to 4 in which the
polysiloxane oil amount of each photosensitive layer is in the range of
about 0.005% by mass to about 0.021% by mass with respect to the total
mass of the materials in the photosensitive layer, good leveling property
is obtained, and the reduction in surface potential after performing the
endurance printing for 1 hour is small and stable, so that an image
defect is less likely to occur.

[0117] In the positive charging single-layer electrophotographic
photoconductor produced in each of Comparative Examples 1 and 2 in which
the polysiloxane oil amount of each photosensitive layer is less than
0.005% by mass with respect to the total mass of the materials, the
reduction in surface potential after performing the endurance printing
for 1 hour is small and stable, so that an image defect is less likely to
occur. However, the leveling property is poor because the crater is
formed on the surface of the photosensitive layer.

[0118] In the positive charging single-layer electrophotographic
photoconductor produced in each of Comparative Examples 3 and 4 in which
the polysiloxane oil amount of each photosensitive layer exceeds 0.021%
by mass with respect to the total mass of the materials, good leveling
property is obtained. However, a significant reduction in the surface
potential of the positive charging single-layer electrophotographic
photoconductor after performing the endurance printing for 1 hour is
observed, and image defects, such as a fog on the background and
nonuniformity of a gray image, occurred.

[0119] Having thus described in detail embodiments of the present
disclosure, it is to be understood that the subject matter disclosed by
the foregoing paragraphs is not to be limited to particular details
and/or embodiments set forth in the above description, as many apparent
variations thereof are possible without departing from the spirit or
scope of the present disclosure.

Patent applications by KYOCERA MITA CORPORATION

Patent applications in class Product having layer between radiation-conductive layer and base or support

Patent applications in all subclasses Product having layer between radiation-conductive layer and base or support